The present invention relates to a control system for a continuously variable transmission (CVT).
Previously, there have been various methods to control the reduction ratio in the CVT. The most popular way is to define a desired engine speed in response to throttle opening degree and vehicle speed and then control a reduction ratio of the CVT to adjust the actual engine speed to achieve the desired engine speed. JP-A 61-105351 uses a predetermined engine speed map which contains various desired engine speed values against various throttle opening degrees and vehicle speeds and defines a desired engine speed using this predetermined map.
What is encountered as difficulty to overcome is to suppress overshoot of the engine speed due to hydraulic delay after a ratio control element has moved off from one reduction ratio command position to another reduction ratio command position. For example, during acceleration from the maximum reduction ratio, there occurs a delay in pressure build-up in a driver pulley cylinder chamber, causing the engine speed to keep increasing until a new smaller reduction ratio is established upon elapse of the delay after the ratio control element has moved off from the maximum reduction ratio command position. Upon attainment of the new reduction ratio, the engine speed is decreased to achieve a new desired engine speed corresponding to the new reduction ratio.